The production of polymers through utilization of renewable resources has been a field of increasing interest for many years. For example, great interest has been shown in polymers formed from lactic acid. Lactic acid occurs in nature via fermentation of carbohydrates such as glucose, sucrose, and lactose. Lactic acid is commercially produced by fermentation of whey, cornstarch, potatoes, molasses, and the like. In forming lactic acid-based polymers, the lactic acid is first oligomerized then depolymerized to form lactide monomer which is then polymerized to high molecular weight polylactide or polylactic acid (PLA). According to current commercial processes, the lactide is processed so as to obtain high purity L-lactide, which is then subjected to a ring-opening polymerization process to form the product crystalline polymers. Polymers formed to date derived from D-lactide and meso-lactide monomers have been shown to be more amorphous, and thus D- and meso-lactide polymers have not been considered to be particularly useful for commercial applications, and particularly in applications in which high semi-crystalline thermoplastic polymer performance characteristics (e.g., high strength, high glass transition temperature (Tg), etc.) are required.
The polymers obtained to date including renewable resource-derived materials tend to have very limited applications, though some polylactide products based upon L-lactide alone such as those commercialized by Natureworks, LLC are beginning to show possible application in some fiber and film technologies. Attempts to include materials derived from renewable resources in broader-based applications have been limited due to cost considerations as well as due to loss of critical properties of the polymeric product upon replacement of the traditional components with the renewable resource derived intermediates. For example, the hydrolytic stability of polymers formed from renewable resources is often such that they degrade too quickly during use, rendering them unsuitable for many applications. Other problems encountered include unacceptable increase in the viscosity of resins upon alteration or removal of the traditional components and unacceptable loss of mechanical and thermal properties, e.g., glass transition temperature, modulus, and strength characteristics, upon inclusion of the renewable resource derived components.
What is needed in the art are polymeric materials that can include monomers, oligomers, polymer blocks, and even entire polymers derived from renewable resources. Moreover, what is needed in the art are polymeric materials incorporating these components that can exhibit qualities suitable for use in applications currently employing materials derived exclusively from non-renewable resources such as traditional vinyl ester-styrene resins.